<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id='app'></div>
</body>
<script>
    let data = {
        msg: 'xxx'
    }
    let vm = {};
    Object.defineProperty(vm, 'msg', {
        // enumerable:true,
        // configurable:true,
        get() {
            console.log(data.msg)
            return data.msg
        },
        set(newValue) {
            if (data.msg === newValue) {
                return
            }
            data.msg = newValue;
            document.getElementById('app').innerHTML=vm.msg
        }
    })
</script>

</html>